This invention relates generally to improvements in a motor driven spindle for driving a disk pack and more particularly, but not by way of limitation, to an improved spring-loaded spindle lock shaft.
In a prior art disk drive apparatus, a disk pack includes a mounting plate attached to the bottom of the pack. The mounting plate has associated with it a threaded screw which is threaded inside the top of a spring-loaded spindle lock shaft. The shaft is disposed inside the center portion of a spindle. When the mounting plate is secured to the spindle, a pin inside the shaft trips an interlock system in the pack allowing a disk pack cover to be removed. The apparatus is then ready for operation.
It has been found that even though the interlock system may be tripped, the mounting plate may not be securely tightened inside the shaft. When this occurs, due to unavoidable tolerances in the threading of the screw and threaded bore of the shaft, the threads allow play which is sufficient to cause torque forces at an angle to the normally concentric axis of the disk pack and spindle. Because the shaft is rigid, it does not compensate for these torque forces. Consequently, distortion occurs in the mounting plate producing eccentricity of the disk pack as the pack is rotated on the spindle. Often the disk drive servo system does not have a high enough frequency response to accurately follow the eccentricity of the disk pack.
Also, the top of the shaft and the base of the threaded screw may contain slight machine imperfections. These imperfections, although small and often undetected during maching inspections, are large enough to cause torque forces when the base is tightened against the top of the shaft. These torque forces are at an angle to the concentric axis of the pack and the shaft. Again, because the shaft is rigid, distortion occurs in the mounting plate producing eccentricity of the disk pack.